TPS73601 datasheet(13/27 Pages) TI

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Reverse Current

Power Dissipation

Thermal Protection

+ (VIN * VOUT)

OUT

(6)

Package Mounting

TPS736xx

SBVS038K – SEPTEMBER 2003 – REVISED SEPTEMBER 2005

expected ambient temperature and worst-case load.

The NMOS pass element of the TPS736xx provides

The internal protection circuitry of the TPS736xx has

inherent protection against current flow from the

been designed to protect against overload conditions.

output of the regulator to the input when the gate of

It was not intended to replace proper heat sinking.

the pass device is pulled low. To ensure that all

Continuously running the TPS736xx into thermal

charge is removed from the gate of the pass element,

shutdown will degrade reliability.

the enable pin must be driven low before the input

voltage is removed. If this is not done, the pass

element may be left on due to stored charge on the

The ability to remove heat from the die is different for

gate.

each package type, presenting different consider-

After the enable pin is driven low, no bias voltage is

ations in the PCB layout. The PCB area around the

needed on any pin for reverse current blocking. Note

device that is free of other components moves the

that reverse current is specified as the current flowing

heat from the device to the ambient air. Performance

out of the IN pin due to voltage applied on the OUT

data for JEDEC low and high K boards are shown in

pin. There will be additional current flowing into the

the Power Dissipation Ratings table. Using heavier

OUT pin due to the 80k

Ω internal resistor divider to

copper will increase the effectiveness in removing

ground (see Figure 1 and Figure 2).

heat

from

the

device.

The

addition

plated

through-holes to heat-dissipating layers will also im-

For the TPS73601, reverse current may flow when

prove the heat-sink effectiveness.

VFB is more than 1.0V above VIN.

Power dissipation depends on input voltage and load

conditions. Power dissipation is equal to the product

of the output current times the voltage drop across

Thermal protection disables the output when the

the output pass element (VIN to VOUT):

junction temperature rises to approximately 160°C,

allowing the device to cool. When the junction tem-

perature cools to approximately 140°C, the output

Power dissipation can be minimized by using the

circuitry is again enabled. Depending on power dissi-

lowest possible input voltage necessary to assure the

pation, thermal resistance, and ambient temperature,

required output voltage.

the thermal protection circuit may cycle on and off.

This limits the dissipation of the regulator, protecting

it from damage due to overheating.

Any tendency to activate the thermal protection circuit

Solder

pad

footprint

recommendations

for

the

indicates excessive power dissipation or an inad-

TPS736xx are presented in Application Bulletin

equate heat sink. For reliable operation, junction

Solder Pad Recommendations for Surface-Mount De-

temperature should be limited to 125°C maximum. To

vices (AB-132), available from the Texas Instruments

estimate the margin of safety in a complete design

web site at www.ti.com.

(including heat sink), increase the ambient tempera-

ture until the thermal protection is triggered; use

worst-case loads and signal conditions. For good

reliability, thermal protection should trigger at least

35°C above the maximum expected ambient con-

dition of your application. This produces a worst-case

junction

temperature

125°C

the

highest

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